Dielectric ceramic composition, ceramic capacitor using the composition and method of producing thereof

ABSTRACT

The present invention provides a dielectric ceramic composition, a capacitor using the composition and the producing method, of having a lower dielectric loss and a stable characteristics in high frequency bandwidth, and enabling to use a base metal or a carbon-based material as an electrode material by allowing sintering at a low temperature, thereby resulting in lower cost.  
     The dielectric ceramic composition according to present invention, is characterized in comprising a main component of formula Sr x Mg 1-x (Zr y Ti 1-y )O 3  (where 0.8≦x≦1; 0.9≦y≦1) to which MnO 2  of 0.05-15 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi 2 O 3 , PbO and Sb 2 O 3  and a glass component of 0.5-15 wt % are added based on the weight of the main component.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a dielectric ceramiccomposition, more particular to a dielectric ceramic composition, aceramic capacitor using the composition and the producing method,thereof having a lower dielectric loss and stable characteristics inhigh frequency bandwidth, and enabling to use a base metal (eg. Cu, Wetc.) or a carbon-based material as an electrode material by allowingsintering at a low temperature, and thereby reducing the productioncost.

[0002] Conventionally, a dielectric property of a ceramic provides aceramic capacitor having larger capacitance and being more miniature insize. The ceramic capacitor may be made of a material selected from TiO₂having a rutile structure, BaTiO₃, MgTiO₃, CaTiO₃ and SrTiO₃, having aperovskite structure and the mixture thereof.

[0003] This ceramic capacitor may be classified into a platelike typeand a laminate type. The platelike type capacitor is produced by formingsaid material powder into some shaped body, such as pellet (disc), rod(cylinder) or chip (angular), under pressure, sintering the shaped bodyat 1200° C.-1400° C. to a sintered body, and forming electrode at eachsurface of the sintered body.

[0004] Also, the laminated type ceramic capacitor is produced by mixingsaid material powder with organic binder and organic solvent to preparea slurry, forming green sheets from the slurry through a doctorbladding, printing the pattern of electrode comprising of a noble metal,such as Pt and Pd, on each of the green sheets, subsequently laminatingsaid green sheets in the thickness direction under pressure to form alaminate, and sintering the laminate at 1200° C.-1400° C.

[0005] As described above, however, in the conventional ceramiccapacitor, the sintering process must be performed at a high temperatureranging 1200° C.-1400° C., to obtain the sintered body exhibiting a goodelectric characteristics and having a high density.

[0006] For the laminated ceramic capacitor, particularly, in the case ofusing a base metal as an electrode material, there has been a problem tooxidize the base metal during the sintering process, which occurs a highresistance layer formation between the ceramic layers. To avoid theproblem, the noble metal material, being stable at high temperature,must be employed as an electrode material, thereby resulting in highcost.

[0007] On application of a device for high frequency bandwidth, such asmicrowave, it is preferred to have a low dielectric loss. And suchdevice is required to have a good electric characteristics such as aquality value (Q), temperature property (this term means temperaturechanging ratio of the capacity), and a high reliability. However, nocurrent dielectric material meets all the conditions.

[0008] Accordingly, there has been a need in the art to provide adielectric ceramic composition, ceramic capacitor using the compositionand the producing method to solve the problem as described above.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a dielectricceramic composition and a producing method of the dielectric ceramiccomposition of having a lower dielectric loss and a stablecharacteristics in high frequency bandwidth, and enabling to use a basemetal, such as Cu and W, or a carbon-based material as an electrodematerial by allowing sintering at a low temperature, thereby reducingthe production cost.

[0010] To achieve the above object, the present invention provides thedielectric ceramic composition comprising a main component of formulaSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1) to which0.05-15 wt % of MnO₂, 0.001-5 wt % of at least one selected from thegroup consisting of Bi₂O₃, PbO and Sb₂O₃ and 0.5-15 wt % of a glasscomponent are added based on the weight of the main component.

[0011] It is another object of the present invention to provide aceramic capacitor using the composition and a method of manufacturingthe ceramic capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are notlimitative of the present invention and wherein:

[0013]FIG. 1 illustrates cross-sectional structural views of a platelikeceramic capacitor in accordance with example 1.

[0014]FIG. 2 illustrates cross-sectional structural views of a laminatedceramic capacitor in accordance with example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0015] According to the present invention, the dielectric ceramiccomposition is characterized ill comprising a main component of formulaSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1), to which MnO₂of 0.05-15 wt %, at least one of 0.001-5 wt % selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃, and a glass component of 0.5-15 wt %are added based on the weight of the main component.

[0016] In the preferred embodiment, the dielectric ceramic compositionis produced by adding MnO₂ of 0.05-15 wt %, at least one of 0.001-5 wt %selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glasscomponent 0.5-15 wt % based on the weight of the component to a maincomponent of formula Sr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1;0.9≦y≦1). The resulting composition can exhibit a high dielectricconstant, a good temperature property and a high quality value (Q). As aresult, the dielectric ceramic composition is suitable for using at highfrequency bandwidth.

[0017] The mole fraction of Sr is preferably 0.8 (80 mol %) or more,when the composition containing Sr of less than 0.8 is fired at 925°C.-1080° C. The sintering property of the resultant is deteriorated.

[0018] The mole fraction of Ti is preferably 0.1 (10 mol %) or less.When the mole fraction of Ti is more than 0.1, the temperature propertyas well as the quality factor (Q) are deteriorated.

[0019] MnO₂ is added to the main component as a sintering aid agent forenabling to sinter at a low temperature. The amount of the agent ispreferably 0.05-15 wt %. When the amount of MiO₂ is less than 0.05 wt %,it does little function as an additive, resulting in a lower density ofthe sintered body. When the amount of MnO₂ is more than 15 wt %, thequality value is deteriorated.

[0020] A metal oxide having a low melting point is added to the maincomponent for improving the temperature property. The metal may be atleast one selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃.The additive amount is preferably 0.001-5 wt %. When the additive isless than 0.001 wt %, the temperature property cannot be improved. Whenthe additive is more than 5 wt %, the quality value is deteriorated.

[0021] The glass component is added thereto as a sintering aid agent forenabling to sinter at a low temperature. The additive amount ispreferably 0.5-15 wt %. When the glass component is less than 0.5 wt %,the temperature property cannot be improved. When the glass component ismore than 15 wt %, the quality value is deteriorated.

[0022] The glass component employed in the present invention preferablyhas a good wettability to the main componentSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1, 0.9≦y≦1) and issoftened and/or melted at 925-1080° C. Specifically, such glasscomponent may be ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.

[0023] In second embodiment of the present invention, SiO₂ of 0.01-5 wt% and Al₂O₃ of 0.01-5 wt % based on the weight of the main component arefurther added to the dielectric ceramic composition to provide anotherdielectric ceramic composition.

[0024] SiO₂ is used as an additive for improving the temperatureproperty. The amount of SiO₂ is preferably about 0.01-5 wt %. When theamount of SiO₂ is less than 0.01 wt %, the temperature property cannotbe improved. When the amount of SiO₂ is more than 5 wt %, the qualityvalue is deteriorated.

[0025] Al₂O₃ is used as an additive for improving the quality value. Theamount of Al₂O₃ is preferably about 0.01-5 wt %. When the amount ofAl₂O₃ is less than 0.01 wt %, the quality value cannot be improved. Whenthe amount of Al₂O₃ is more, than 5 wt %, the temperature property isdeteriorated.

[0026] In the third embodiment of the present invention, a rare earthoxide of 0.001-2 wt % is further added to the dielectric ceramiccomposition to provide another dielectric ceramic composition based onthe weight of the main component.

[0027] The rare earth oxide is used as an additive for improving thetemperature property. Preferably, the amount of the rare earth oxide isabout 0.001-2 wt %. When the amount of the rare earth oxide is less than0.001 wt %, the temperature property cannot be improved. When the amountof the rare earth oxide is more than 2 wt %, the quality value isdeteriorated.

[0028] The rare earth oxide employed in the present invention haspreferably a good wettability to the main compositionSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1) and has agrain boundary layer, which is used to improve the sintering property.Specifically, such rare earth oxide may include at least one selectedfrom the group consisting of La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃,Ho₂O₃, Er₂O₃, Tm₂O₃ and Yb₂O₃.

[0029] Also, the present invention provides a ceramic capacitor with theopposed surfaces comprising one of the dielectric ceramic compositionsas described above, each of which an electrode is formed on. Theelectrode of the ceramic capacitor may be base metal or carbon-basedmaterial, since the capacitor can be produced through sintering at thelow temperature.

[0030] Further, the present invention provides a ceramic capacitor madeby laminating alternatively electrodes and sheets comprising one of thedielectric ceramic compositions as describe above.

[0031] The ceramic capacitor according to the present invention exhibitsa lower dielectric loss and stable characteristics, by using one of thedielectric ceramic compositions as describe above. Therefore, theceramic capacitor is expected to have more improved reliability.Moreover, it is advantageous that the dielectric ceramic composition canbe sintered at a low temperature of 925-1080° C. Therefore, aninexpensive metal, such as a base metal and a carbon-based material, canbe used as an internal electrode, thereby reducing the production cost.

[0032] The base metal having a good conductibility and a highreliability is preferably employed as the electrode, which may be atleast one selected from the group consisting of Cu, Ni, W and Mo, andthe carbon-based material employed as the electrode may be carbon(amorphous), graphite or the mixture.

[0033] In present invention, a ceramic capacitor fabricating methodcomprises the steps of forming powder comprising a main component offormula Sr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1), towhich MnO₂ of 0.05-15 wt %, at least one of 0.001-5 wt % selected fromthe group consisting of Bi₂O₃, PbO and Sb₂O₃, and a glass component of0.5-15 wt % are added based on the weight of the main component, into abulk or a sheet; and sintering the bulk or a sheet at about 925-1080° C.

[0034] According to the method, a sintering aid agent of MnO₂ and glasscomposition can improve a wettability of a grain boundary layer to bindpowder particles and reduce the void fraction during the sinteringprocess even at low temperature of about 925-1080° C. Thus, the sinteredbody having a high strength and high density can be obtained at the lowtemperature.

[0035] In another embodiment of the present method, the method maycomprise the additional step of providing an electrode on a main surfaceof the sheet; laminating the sheet in the thickness direction underpressure to form a laminate; and sintering the laminate at about925-1080° C.

[0036] According to this method, a base metal, such as Cu and Ni, or acarbon-based material, such as amorphous carbon and graphite, is used asan internal electrode, which is less expensive than noble metal, such asPt and Pd, resulting in the lower cost without deteriorating thecharacteristics.

[0037] The embodiments of the present invention will now be described byway of example.

EXAMPLE 1

[0038] Referring to FIG. 1, cross-sectional structural view of aplatelike ceramic capacitor in accordance with a first example is shownin FIG. 1. The capacitor comprises a bulk shape dielectric body 1,terminal electrodes 2 formed on the opposed surfaces of the dielectricbody 1, lead lines 3 connecting to the terminal electrode, and an epoxyresin 4 encapsulating the dielectric body 1 and the terminal electrode2.

[0039] The dielectric body 1 is made of a dielectric ceramic compositioncomprising a main component of formula Sr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃(where 0.8≦x≦1; 0.9≦y≦1), to which MnO₂ of 0.05-15 wt %, at least one of0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃and a glass frit (glass component) of 0.5-15 wt % are added based on theweight of the main component.

[0040] The dielectric body 1 may include one of to the dielectricceramic composition further containing SiO₂ of 0.01-5 wt % and Al₂O₃ of0.01-5 wt %, the dielectric ceramic composition further containing arare earth oxide of 0.001-2 wt %, and the dielectric ceramic compositionfurther containing SiO₂ of 0.01-5 wt %, Al₂O₃ of 0.01-5 wt % and rareearth oxide of 0.001-2 wt %.

[0041] The terminal electrode 2 comprises a conductive material having ahigh reliability, such as Ag and Ag alloy. Preferably, Ag alloy mayinclude 90Ag-10Pd. The material of the terminal electrode 2 may alsoinclude at least one selected from the group consisting of Cu, Ni, W andMo, or carbon, graphite or the mixture.

[0042] This ceramic capacitor exhibits a stable dielectric constant (ε),quality factor (Q) and temperature property (Tc) even in high frequencybandwidth.

[0043] The method of manufacturing this capacitor will now be described.

[0044] Each of Powdered SMZT, MnO₂, at least one selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃, glass frit, SiO₂, Al₂O₃ and rareearth oxide were weighed as the predetermined amount.

[0045] In this example, each of powderedSr_(0.95)Mg_(0.05)(Zr_(0.95)Ti_(0.05))O₃, MnO₂, PbO, glass component(ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass), SiO₂, Al₂O₃ andLa₂O₃ was weighed to prepare a dielectric ceramic composition as shownin Table 1. TABLE 1 Main component (mole fraction) Additive A Additive BSintering Speci- Sr_(x)Mg_(1−x)(Zr_(y)Ti_(1−y))O₃ (wt %) (wt %)temperature men Sr Mg Zr Ti MnO₂ Al₂0₃ SiO₂ Glass frit PbO La₂O₃ (° C.) 1 1 0 1 0 0 0 0 0 0 0 1050  2 1 0 1 0 0.3 0 0 0.5 1.0 0 1000  3 1 0 10 0.3 0 0 3.0 1.0 0 950  4 1 0 1 0 0.3 0 0 11.0 1.0 0 950  5 1 0 0.950.05 5.0 0.1 0.05 2.5 0.5 0.01 950  6 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.50.01 1000  7 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 900  8 1 0 0.950.05 5.0 0.1 0.05 2.5 8.0 0.01 950  9 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.50.01 950 10 0.98 0.02 0.95 0.05 5.0 0.05 0.05 2.6 0.5 0.01 950 11 0.980.02 0.95 0.05 5.0 0.5 0.05 2.5 0.5 0.01 950 12 0.98 0.02 0.95 0.05 5.00.5 0.05 2.5 1.0 0.01 900 13 0.98 0.02 0.95 0.05 5.0 0.5 0.05 11.0 1.00.01 950 14 0.98 0.02 0.95 0.05 5.0 5.0 0.05 2.5 0.5 0.01 950 15 0.980.02 0.95 0.05 5.0 0.1 0.5 2.5 0.5 0.01 950 16 0.95 0.05 0.95 0.05 0.040 0 3.5 0 0 925 17 0.95 0.05 0.95 0.05 2.6 0 0 0.4 0 0 925 18 0.95 0.050.95 0.05 2.5 0 0 3.5 0 0 925 19 0.95 0.05 0.95 0.05 3 0.2 0.3 0.4 0.50.00 950 20 0.95 0.05 0.95 0.05 5 0.1 0.06 5 0.5 0.03 900 21 0.95 0.050.95 0.05 5 0.1 0.05 5 0.5 0.03 950 22 0.96 0.05 0.95 0.05 5 0.05 0.06 50.5 0.03 975 23 0.95 0.05 0.95 0.05 5 0.5 0.05 5 0.5 0.03 975 24 0.950.05 0.95 0.05 6 5.0 0.06 5 0.5 0.03 976 25 0.95 0.05 0.95 0.05 5 0.10.5 5 0.5 0.03 975 26 0.95 0.05 0.95 0.05 5 0.1 5.0 5 0.6 0.03 975 270.95 0.06 0.95 0.05 5 0.1 0.1 5 0.5 0.03 1050 28 0.8 0.2 0.95 0.05 5 0.10.05 3.5 0.5 0.03 950 29 0.8 0.2 0.95 0.05 5 0.1 0.05 5 0.5 0.03 900 300.75 0.25 0.95 0.05 5 0.1 0.05 5 0.5 0.03 950

[0046] The prepared components were wet-milled with water or organicsolvent such as ethanol and acetone) in ball mill for predeterminedtime, such as 24 hours. The resultant mixture was dehydrated (or removalof the solvent, such as ethanol and acetone) and dried. Specimencomprising different composition from thereof the present invention wasprepared as comparison (indicated by  in the Table 1).

[0047] Then, dried mixture was preliminary fired at 550-750° C., for05-5.0 hours, followed by pulverizing for 1-24 hour with a mortarmachine (or automatic pestle) to obtain the fired powder having thedesired granularity.

[0048] Subsequently, an appropriate amount of an organic binder wasadded to the fired powder. The resultant was mixed and granularizeduniformly using a mortar machine and a like to obtain granular powderhaving the desired granularity. Polyvinyl alcohol (PVA) was employed asa organic binder. Other organic binder may include ethylcelluloseaqueous solution and acryl resin solution (acryl binder)

[0049] Then, the pellet having a diameter of 20 mm and a thickness of0.5 mm is formed from the granular powder using a forming machine,followed by firing at 925-1080° C., for 0.5-10 hours under atmosphere,to obtain a disk-shaped dielectric body 1.

[0050] The composition of the present invention was fired at the othertemperature to prepare another specimen as comparison (indicated by  inthe Table 1).

[0051] Table 2 shows electric characteristics of each specimen, and thecomparison is indicated by “”. TABLE 2 Temperature Specimen DielectricQuality Resistance property (Tc) number constant (ε) value (Q) (Ω · cm)(ppm/° C.)  1 13  230 1.6 × 10¹¹ 96 2 19  950 1.3 × 10¹² 93 3 23 23001.9 × 10¹² 60  4 22  380 1.5 × 10¹² 180  5 28 2680 1.7 × 10¹² 58 6 273630 1.5 × 10¹² 63 7 24  190 1.6 × 10¹² 56 8 33  180 1.5 × 10¹² 26 9 316000 2.0 × 10¹² 35 10  29 2670 1.8 × 10¹² 38 11  27 2980 1.6 × 10¹² 3212 12  310 1.5 × 10¹² 15 13 28  60 1.8 × 10¹² 27 14  26  790 1.9 ×10¹² 43 15  25 2340 2.0 × 10¹² 36 16 18  370 1.9 × 10¹² 32 17 16  2702.1 × 10¹² 27 18  23 2560 1.8 × 10¹² 68 19 12  320 1.6 × 10¹² 71 20 17 150 1.3 × 10¹¹ 29 21  25 1700 2.2 × 10¹² 75 22  25 2550 2.1 × 10¹² 5823  22 2500 1.7 × 10¹² 82 24  26 2700 1.1 × 10¹³ 105  25  24 2300 1.9 ×10¹² 74 26  22 1970 1.5 × 10¹² 23 27  23 2200 2.1 × 10¹² 63 28  17 12902.0 × 10¹² 32 29 12  200 1.8 × 10¹² 17 30 11  170 1.9 × 10¹² 40

[0052] Wherein, the dielectric constant (ε) was measured at 25° C. underthe condition of frequency of 1 MHz and an input voltage of 1V_(rms).The Q value was measured under the condition of frequency of 1 MHz andan input voltage of 1V_(rms). The temperature property (Tc) wascalculated from the following equation

Tc(ppm/° C.)=(C 2−C 1×10⁶)/(C 1×(125−25))

[0053] Wherein, the C1 is the capacitance at 125° C. and the C2 is thecapacitance at 25° C.

[0054] And the resistance (R(Ω×cm)) was calculated by using the voltageand the current, which were measured on applying a direct voltage of1000V for 1 minute at 25° C.

[0055] Referring to the result of Table 2, the dielectric constant (ε),Q value and temperature property (Tc) were stable even at high frequencyin this example, while the characteristics of all the comparisons weredeteriorated.

[0056] Further, when the specimen surfaces of these examples wereobserved through a metallurgical microscope, it will be known that novoid was present at grain boundary and a dense sintering body wasconstructed.

[0057] As described above, according to this example, the dielectriccomposition exhibiting high dielectric constant, high Q value and goodtemperature property, can be obtained by adding MnO₂ of 0.05-15 wt %, atleast one of 0.001-5 wt % selected from the group consisting of Bi₂O₃,PbO and Sb₂O₃ and a glass frit 0.5-15 wt % to a main component of SMZTbased on the weight of the main component and optionally further addingSiO₂ of 0.01-5 wt % and Al₂O₃ of 0.01-5 wt % and rare earth oxide of0.001-2 wt % thereto. Thus, the dielectric composition is capable of adielectric capacitor having stable characteristics and improvedreliability.

[0058] According to the method of manufacturing the ceramic capacitor,the ceramic capacitor having high density and strength can be providedat the low temperature by forming a bulk or a sheet from powdercomprising a main component of SMZT to which MnO₂ of 0.05-15 wt %, atleast one 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbOand Sb₂O₃ and a glass component of 0.5-15 wt % are added based on theweight of the component, and which optionally SiO₂ of 0.01-5 wt % andAl₂O₃ of 0.01-5 wt % and rare earth oxide of 0.001-2 wt % are addedthereto and firing the sheet or other resultant at 925-1080° C.

EXAMPLE 2

[0059]FIG. 2 illustrates cross-sectional structural view of a laminatedceramic capacitor in accordance with second example. The capacitorcomprises a sheet-shaped dielectric layers 11, thin internal electrodes12 and terminal electrodes 13,14. This laminated ceramic capacitor iscomprised of eight dielectric layers 11 and seven thin internalelectrodes 12, which are alternatively laminated.

[0060] The dielectric layer 11 is made of sheet-shaped ceramiccomposition comprising a main component of SMZT to which MnO₂ of 0.05-15wt %, at least one of 0.001-5 wt % selected from the group consisting ofBi₂O₃, PbO and Sb₂O₃ and a glass frit (glass component) of 0.5-15 wt %are added based on the weight of the main component.

[0061] Alternatively, the dielectric layer 11 may include one of thedielectric ceramic composition further containing SiO₂ of 0.01-5 wt %and Al₂O₃ of 0.01-5 wt %, the dielectric ceramic composition furthercontaining rare earth oxide of 0.001-2 wt %, and the dielectric ceramiccomposition further containing SiO₂ of 0.01-5 wt %, Al₂O₃ of 0.01-5 wt %and rare earth oxide of 0.001-2 wt % is added.

[0062] The internal electrode 12 and the terminal electrodes 13, 14include a conductive material having high reliability, for example, Cu,Ni, W and Mo, or carbon, graphite or the mixture.

[0063] This laminated ceramic capacitor exhibits a stable dielectricconstant (ε), quality factor (Q) and temperature property (Tc) even inRF region.

[0064] The method of manufacturing this laminated ceramic capacitor willbe described now.

[0065] Each of powdered SMZT, MnO₂, at least one selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃, glass frit, SiO₂, Al₂O₃ and rareearth oxide were weighed as the predetermined amount. Each compositionwas wet-milled with water (or organic solvent such as ethanol andacetone) in ball mill for predetermined time, such as 24 hours. Theresultant mixture was dehydrated (or removal of the solvent, such asethanol and acetone) and dried. Specimens comprising differentcompositions from thereof the present invention were prepared ascomparisons (indicated by  in the Table 1).

[0066] Then, an appropriate amount of an organic binder was added to thedried powder. Subsequently, the resultant powder was mixed using amortar machine, a mixing mill and a like to obtain a slurry havingdesired viscosity. Polyvinyl alcohol (PVA) was employed as the organicbinder. Other organic binder may be employed, such as ethylcelluloseaqueous solution and acryl resin solution (acryl binder).

[0067] Then, the slurry was deaired and formed into sheets throughdoctor blading to obtaining a ceramic green sheet. A conductive pastewas printed as desired pattern on the green sheet. Thereby the internalelectrode layer was formed on the green sheet. The conductive paste mayinclude alloy containing at least one selected from a group consistingof Cu, Ni, W and Mo, or carbon, graphite or the mixture.

[0068] Particularly, the conductive paste employed in present inventionmay be a carbon paste made from a mixture powder of a carbon powder anda graphite powder, W paste and Mo paste, as well as a Cu paste, which isobtained by adding organic binder, dispersing agent, organic solventand, if necessary, reducing agent, to Cu powder and then mixing thereof.

[0069] Then, the green sheets were laminated in the thickness directionunder pressure to form a laminate, followed by firing at 925-1080° C.,under inert gas atmosphere, such as N₂ gas, or N₂—H₂ reductiveatmosphere. Each terminal electrode was formed on the opposed sides ofthe laminate. Thus, the laminated ceramic capacitor can be producedthrough the step of laminating alternatively the dielectric layer 11 andthe internal electrode 12.

[0070] As described above, for the laminated ceramic capacitor accordingto this example, it can exhibit high dielectric constant, high Q valueand good temperature property, since it is comprised of the compositionobtained by adding MnO₂ of 0.05-15 wt %, at least one of 0.001-5 wt %selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glassfrit of 0.5-15 wt % to a main component of SMZT based on the weight ofthe component and optionally further adding 0.01-5 wt % of SiO₂ and0.01-5 wt % of Al₂O₃ and 0.001-2 wt % of rare earth oxide thereto. Thus,the laminated ceramic capacitor is capable of exhibiting stablecharacteristics and improved reliability in high frequency.

[0071] According to the method of manufacturing the laminated ceramiccapacitor, the laminated ceramic capacitor having high density andstrength can be produced by forming the internal electrode on the greensheet comprising a main component of SMZT to which MnO₂ of 0.05-15 wt %,at least one of 0.001-5 wt % selected from the group consisting ofBi₂O₃, PbO and Sb₂O₃ and a glass component of 0.5-15wt % are added basedon the weight of the component, and which optionally 0.01-5 wt % of SiO₂and 0.01-5 wt % of Al₂O₃ and 0.001-2 wt % of rare earth oxide are addedthereto, laminating the green sheet in the thickness direction to form alaminate, firing the laminate at 925-1080° C. under inert gas atmosphereor N₂—H₂ seductive atmosphere. Thus, an inexpensive base metal andcarbon-based material can be used as an electrode material, in lie of anoble metal, such as Pt or Pd, since the laminated ceramic capacitor isproduced by the process of firing at relatively low temperature.Therefore, the manufacturing method according to the present inventioncan realize the lower cost without deteriorating the characteristics.

[0072] As described above, according to the dielectric ceramiccomposition of the present invention, the dielectric composition isproduced by adding MnO₂ of 0.05-15 wt %, at least one of 0.001-5 wt %selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glassfrit of 0.5-15 wt %, to a main component of SMZT based on the weight ofthe component and optionally further adding 0.01-5 wt % of SiO₂ and0.01-5 wt % of Al₂O₃ and 0.001-2 wt % of rare earth oxide thereto. Thus,the dielectric composition can exhibit high dielectric constant, high Qvalue and good temperature property, resulting in the stablecharacteristics and improved reliability at high frequency region, suchas microwave.

[0073] For a ceramic capacitor, according to the present invention, thecapacitor can exhibit a low dielectric loss even at high frequencybandwidth, since it is made of the dielectric ceramic composition.Therefore, the present capacitor is suitable for RF device. The presentcapacitor can also realize the lower cost without deteriorating thecharacteristics, since an inexpensive base metal or carbon-basedmaterial can be used as an electrode material due to the low sinteringtemperature of 925-1080° C.

[0074] While the invention has been described in its preferredembodiments, this should not be construed as limitation on the scope ofthe present invention and can be modified and changed to other variousembodiments. Accordingly, the scope of the present invention should bedetermined not by the embodiments illustrated, but by the appendedclaims and their legal equivalents. In second example, eight dielectriclayers and seven internal electrodes are laminated to form a laminate,but the number of the dielectric or internal electrode may be changed tobe suitable for the desired capacitor and characteristics.

What is claimed is:
 1. A dielectric ceramic composition, comprising amain component of formula Sr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where0.8≦x≦1; 0.9≦y≦1), MnO₂ of 0.05-15 wt %, at least one of 0.001-5 wt %selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃, and a glasscomponent of 0.5-15 wt %, based on the weight of the main component. 2.The dielectric ceramic composition according to claim 1, furthercomprising SiO₂ of 0.01-5 wt % and Al₂O₃ of 0.01-5 wt %.
 3. Thedielectric ceramic composition according to claim 1, further comprisinga rare earth oxide of 0.001-2 wt %.
 4. The dielectric ceramiccomposition according to claim 2, further comprising a rare earth oxideof 0.001-2 wt %.
 5. The dielectric ceramic composition according toclaim 1, wherein the glass component is ZnO—SiO₂ based glass orLi₂O—Al₂O₃—SiO₂ based glass.
 6. The dielectric ceramic compositionaccording to claim 2, wherein the glass component is ZnO—SiO₂ basedglass or Li₂O—Al₂O₃—SiO₂ based glass.
 7. The dielectric ceramiccomposition according to claim 3, wherein the glass component isZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.
 8. The dielectricceramic composition according to claim 4, wherein the glass component isZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.
 9. The dielectricceramic composition according to claim 3, wherein the rare earth oxideis at least one selected from the group consisting of La₂O₃, CeO₂,Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, and Yb₂O₃.
 10. Thedielectric ceramic composition according to claim 4, wherein the rareearth oxide is at least one selected from the group consisting of La₂O₃,CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, and Yb₂O₃.
 11. Aceramic capacitor comprising: a ceramic body of the dielectric ceramiccomposition according to claim 1; and electrodes formed respectively onopposed surfaces of the ceramic body.
 12. The ceramic capacitoraccording to claim 11, wherein said electrode is base metal orcarbon-based material.
 13. A ceramic capacitor comprising: a ceramicbody of the dielectric ceramic composition according to claim 2; andelectrodes formed respectively on opposed surfaces of the ceramic body.14. A ceramic capacitor comprising: a ceramic body of the dielectricceramic composition according to claim 3; and electrodes formedrespectively on opposed surfaces of the ceramic body.
 15. A ceramiccapacitor comprising: a ceramic body of the dielectric ceramiccomposition according to claim 4; and electrodes formed respectively onopposed surfaces of the ceramic body.
 16. A ceramic capacitorcomprising: a ceramic body of the dielectric ceramic compositionaccording to claim 5; and electrodes formed respectively on opposedsurfaces of the ceramic body.
 17. A ceramic capacitor comprising: aplurality of sheets of dielectric ceramic composition according to claim1; and a plurality of electrodes on each of sheets, wherein the sheetsand the electrodes are alternatively laminated.
 18. The ceramiccapacitor according to claim 17, wherein said electrode is base metal orcarbon-based material.
 19. A method of producing a dielectric ceramiccomposition, comprising the steps of: forming a bulk or a sheet withpowder including a main component of formulaSr_(x)Mg_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.8≦x≦1; 0.9≦y≦1), to which MnO₂of 0.05-15 wt %, at least one of 0.001-5 wt % selected from the groupconsisting of Bi₂O₃, PbO and Sb₂O₃ and glass component 0.5-15 wt % areadded based on the weight of the main component; and firing the bulk orthe sheet at 925-1080° C.
 20. The method according to claim 10, furthercomprising: providing an electrode on a main surface of the sheet;laminating the sheet in the thickness direction under pressure to form alaminate; and firing the laminate at 925-1080° C.